Catalytic naphtha reforming is an important oil refining process that converts low-octane paraffins- and naphthenes-rich naphtha to high-octane, aromatics-rich C5+ liquid (reformate) and hydrogen (H2). Petroleum refiners are always searching for improved reforming catalysts that afford high selectivity (i.e., high C5+ liquid and H2 yields), high activity, low coking rates and high selectivity and/or activity stability. More selective catalysts are desired to maximize the production of valuable C5+ liquid and H2 while minimizing the yields of less desirable C1-C4 gaseous products. Catalysts with acceptable selectivity but higher activity are also desired because they allow operation at lower reactor inlet temperatures while maintaining the same conversion (octane) level or allow operation at the same temperature but at higher conversion (octane) level. In the former case, the higher activity of the catalysts also allows for significant extension of the cycle length and reduced frequency of regeneration. Catalysts that afford lower coke make rates and higher selectivity and/or activity stability are also very highly desired because they allow for significant shortening of the coke burn off and unit turnaround time or for a longer operation before regeneration.
Many researchers have devoted their efforts to the discovery and development of improved reforming catalysts. The original commercial catalysts employed a platinum-group metal, preferably platinum itself, deposited on a halogen-acidified γ-alumina support; see, for example, Haensel's U.S. Pat. Nos. 2,479,109-110, granted in 1949 and assigned to Universal Oil Products Company. About 1968, the use of rhenium together with platinum was introduced. Kluksdhal's U.S. Pat. No. 3,415,737 teaches Pt/Re catalysts wherein the atomic ratio of rhenium to platinum is between 0.2 and 2.0 and his U.S. Pat. No. 3,558,477 teaches the importance of holding the atomic ratio of rhenium to platinum to less than 1.0. Buss's U.S. Pat. No. 3,578,583 teaches the inclusion of a minor amount, up to 0.1 percent, of iridium in a catalyst having up to 0.3 percent each of rhenium and platinum. Gallagher et al.'s U.S. Pat. No. 4,356,081 teaches a bimetallic reforming catalyst wherein the atom ratio of rhenium to platinum is between 2 and 5.
Phosphorus has been known to increase aromatics yield when included in reforming catalysts since at least 1959 when Haensel taught the same in U.S. Pat. No. 2,890,167. In U.S. Pat. No. 3,706,815, Alley taught that incorporating chelating ions of a Group VIII noble metal with polyphosphoric acid in a catalyst enhances isomerization activity. And Antos et al's U.S. Pat. Nos. 4,367,137, 4,416,804, 4,426,279, and 4,463,104 taught that the addition of phosphorus to a noble-metal reforming catalyst results in improved C5+ yields.
In 1974-5, Wilhelm's U.S. Pat. Nos. 3,798,155, 3,888,763, 3,859,201 and 3,900,387 taught the inclusion of bismuth in a platinum-group reforming catalyst to improve selectivity, activity and stability characteristics. Antos' U.S. Pat. No. 4,036,743 taught a hydrocarbon conversion catalyst comprising platinum, bismuth, nickel and halogen components. More recently, Wu et al's U.S. Pat. Nos. 6,083,867 and 6,172,273 B1 taught a reforming catalyst of mixed composition or stage-loaded catalyst system comprising a first catalyst comprising platinum and rhenium on a porous carrier material and a second catalyst comprising a bismuth and silica components.
Until now, however, no one has taught the unexpected performance benefits of including both bismuth and phosphorus in a noble-metal naphtha reforming catalyst.